MIDI notes not sounding

[mickeyrouse]

I have encountered a curious phenomenon. Some of the MIDI Tracks I have created with Expand/Mini grand intrumrnt plug-in occasionally do not sound. It seems it only happens when a 3 minute or so track is complted or near completed. A visual idicator is that the notes written in have turned from the crisp dark bilue to knida of a fuzzy grayish-blue. Nothing can get the notes to sound. I have tried delting and re-insering the instrument plug-in with no change. At first I was severely peturbed(PO’ed?), thinking multiple spent writing a track was lost. Then I discoverd that I could duplicate the track and upon re’insering the instrument plug-in all is good. This doesn’t seem to happen with other instrument plug-ins such as Superior Drummer or Sample Modeling horns much if any, but it still is a distraction while working on a project. I’m using Windows 7, 8 gig of Ram, intel 5 core processor. The system doesn’t seem to be related, because The number of instruments seems to have no bearing on the problem- it has happened before with only a piano track.
Any ideas?